This invention relates to the production, by thin-layer integrated circuit techniques, of switching circuits which are capable in particular of transmitting or interrupting telephone calls.
At present there are two telephone switching techniques, namely conventional switching and time-division switching.
Time-division switching, in which a position in a "frame" is attributed to each conversation, involves the use of a computer which memorizes the signals representing each conversation and restores them to the appropriate wire in the appropriate order. The invention is not concerned with this technique.
Conventional switching, with which the invention is concerned, comprises physically making or breaking circuits by means of switches, preferably of the automatically controlled type. The four principal techniques currently used for conventional switching are as follows:
SWITCHING WITH ELECTROMECHANICAL RELAYS (FOR EXAMPLE WITH A COIL AND ARMATURE);
SWITCHING WITH SEALED CONTACT RELAYS (SO-CALLED REED RELAYS);
SWITCHING WITH A MATRIX OF ELECTROMECHANICAL RELAYS (CROSSBAR TYPE);
SWITCHING WITH SEMICONDUCTOR CONNECTION CIRCUITS.
Electromechanical relays are expensive and are being used to a diminishing extent.
The crossbar contact matrix is universally used. It is a mechanical assembly which is complex, fragile, heavy, expensive both in regard to purchase price and in regard to energy consumption and, in addition, lacks compactness (100 contacts per cubic decimeter). The reed relay is being used to an ever increasing extent, but requires a lot of special wirings and, in addition, a separate component for each contact.
Semiconductors, have certain disadvantages. Transistors have a waste voltage; thyristors have a high energy consumption and it is still not known to produce them in the monolithic integrated circuit technology.
The present invention does not have any of the disadvantages of the above-mentioned solutions.